<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        select {
            width: 50px;
            float: right;
            margin-bottom: 20px;
        }

        div {
            margin: 50px auto;
            width: 200px;
            height: 200px;
        }
    </style>
</head>

<body>
    <div>
        请选择省份：
        <select>
        </select><br><br>

        请选择地区:
        <select>
            <option></option>
            <option></option>
            <option></option>
            <option></option>
        </select><br><br>

        请选择具体地址：
        <select>
            <option></option>
            <option></option>
            <option></option>
            <option></option>
        </select>
    </div>
    <!-- 引入jQuery链接 -->
    <script src="https://cdn.bootcdn.net/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
    <script>
        // 封装async函数+promise+ajax
        function ajax({ type, url, data }) {
            return new Promise((resolve, reject) => {
                $.ajax({
                    type,
                    url,
                    data,
                    success(result) {
                        resolve([null, result])
                    },
                    error(err) {
                        resolve([err, undefined])
                    }
                })
            })
        }
        async function ale() {
            let [err, val] = await ajax({
                type: 'get', url: 'http://localhost:3000/yi'
            })
            let [err1, val1] = await ajax({
                type: 'get', url: 'http://localhost:3000/er'
            })
            let [err2, val2] = await ajax({
                type: 'get', url: 'http://localhost:3000/san'
            })
        }
        // 调用
        ale()
    </script>
</body>

</html>